The present invention relates to a concentrated winding stator coil for an electric rotary machine.
A concentrated winding stator, conventionally proposed in the field of electric rotary machines, includes a plurality of phase windings each consisting of same phase coils connected with each other and wound in a concentrated manner around respective teeth of a stator core (hereinafter, referred to as tooth coils). From requirements of the winding work, this kind of concentrated winding stator is generally used for an assembled core which is formed by assembling separated partial cores of respective teeth into a stator core.
The tooth coils of a concentrated winding stator are wound around the teeth to have a required turn number. Two neighboring turns are usually disposed to be adjacent to each other in the axial direction on a circumferential surface of the tooth. The winding order for this concentrated winding stator is as follows.
First, the winding work starts from one radial end side of a tooth to the other radial end side of this tooth to arrange a first layer coil. Then, turning the advancing direction, the winding work restarts from the other radial end side of the tooth to the one radial end side of this tooth. Thus, a second layer coil is arranged on the first layer coil. Similarly, a third layer coil is arranged on the second layer coil so as to realize highly densified winding. The first layer coil, the second layer coil, and the third layer coil are collectively referred to as “layer coils”, in the following description.
The Japanese patent application Laid-open No. 2001-186703 discloses, as a tooth coil winding arrangement for a concentrated winding stator, a tooth coil with a starting end disposed at a proximal end portion (or distal end portion) of a tooth and a terminal end disposed at a distal end portion (or proximal end portion) of the tooth. Furthermore, this prior art document discloses, as another tooth coil winding arrangement, a tooth coil with starting and terminal ends being both disposed at the distal end portion of a tooth.
However, the tooth coils disclosed in the above-described prior art document have the following problems.
First, in the process of arranging a phase winding by connecting tooth coils of the same phase via crossovers in serial or parallel to each other, at least one end of each tooth coil is positioned at the distal end portion of the tooth. In the case of using short crossovers, the crossovers or lead wires extending from end portions of the tooth coils and connected to the crossovers will be positioned very closely to the cylindrical surface of a rotor. If these wires are loosened and subjected to vibrations, there will be the possibility that the wires contact with the rotor.
Next, it is necessary to perform the wire connection work at an outer side of an end face of a tooth in the axial direction, for connecting a lead wire extending from a distal end portion (i.e. one end) of this tooth with a lead wire extending from one end of other tooth. Performing such a wire connection work near the tooth coils or slots is not easy.
Next, the arrangement requiring crossovers or lead wires disposed on the tooth coils wound around respective teeth will necessarily increase the axial length of the stator and also increase the armature resistance. These problems are especially serious when a conductor having a large cross-sectional area is used for the tooth coil, because it is necessary to use a comparable conductor having an equivalent cross-sectional area for the crossover intervening between the tooth coils or lead wires of respective tooth coils.
One method for solving these problems is connecting respective tooth coils in parallel with each other to reduce the current flowing in each tooth coil. It will become possible to reduce a required cross-sectional area of a conductor used for the tooth coil. However, to realize this arrangement, it is necessary to increase the turn number of each tooth coil to compensate the loss of magnetic force corresponding to reduction of the current flowing in the tooth coil. According to the concentrated winding stator, the required increase in the turn number should be considered separately for the case that all of the tooth coils of the same phase are connected in parallel with each other as well as for the case that all of the tooth coils of the same phase are connected in serial with each other. If the turn number of the former case is × times as large as that of the latter case while the conductor of the former case is 1/× times as larger in cross-sectional area as that of the latter case, the former case and the latter case should be theoretically identical. However, in the case of connecting all of the tooth coils of the same phase in parallel with each other, it is necessary to coaxially and annularly dispose crossover bus bars of respective phases and neutral bus bars around the stator core. More specifically, the crossover bus bars are used for applying the phase voltages to respective tooth coils. The neutral bus bars form a neutral point. As a result, a large bus bar accommodation space is required.
Furthermore, due to damage or deterioration of a resin coating film of the tooth coil conductor, the possibility of lessening electric insulation properties between neighboring turns of each tooth coil will greatly increase.
Furthermore, coating a thin tooth coil conductor with a resin film and winding this coil conductor densely around a tooth is not preferable in assuring satisfactory cooling properties for the coil conductor positioned deeply in the layers of turns. Namely, the resin coating film of respective tooth coils and numerous clearances between adjacent turns will increase the heat transfer resistance so greatly that large current cannot be supplied to the tooth coil. As a result, the electric rotary machine undesirably increases its size.
For example, to realize a compact and lightweight electric rotary machine having a concentrated winding stator, it is important to increase the cross-sectional area of a tooth coil conductor as far as requirements of the circuit specs are satisfied, shorten a total elongated distance of the armature winding, and bring all turns of the tooth coil into contact with tooth or with cooling air.
To realize such an optimum tooth coil, it will be understood that a desirable tooth coil should have turns of only one layer or two layers wound around a tooth and respective tooth coils of the same phase should be serially connected.
However, in this case, the cross-sectional area of the tooth coil conductor becomes very larger. For example, according to a conventional concentrated winding stator disclosed in the above-described prior art document, the axial length of the concentrated winding stator increases by an amount of the lead wires and the crossovers of tooth coils extending on the tooth coils. As a result, the electric rotary machine undesirably increases its size.